In recent years, there is an increasing demand for higher image quality because color images have become greatly popular. In full-color digital copying machines or printers, a color image original is color-separated with color filters of blue, green and red, and thereafter latent images corresponding to original images are developed with use of developers for respective colors of yellow, magenta, cyan and black. Hence, it follows that the coloring power a colorant has which is contained in the developer for each color has a great influence on image quality.
As typical examples of pigments having high transparency and coloring power for yellow, there are pigments having an isoindolinone skeleton as typified by C.I. Pigment Yellow 185. As to C.I. Pigment Yellow 185, some examples of its application to toners are also known in the art (see PTL 1).